U.S. patent application number 12/552891 was filed with the patent office on 2010-03-04 for method for fabricating a locally passivated germanium-on-insulator substrate.
Invention is credited to Frederic Allibert, Chrystel Deguet, Thomas Signamarcheix.
Application Number | 20100052104 12/552891 |
Document ID | / |
Family ID | 40085584 |
Filed Date | 2010-03-04 |
United States Patent
Application |
20100052104 |
Kind Code |
A1 |
Signamarcheix; Thomas ; et
al. |
March 4, 2010 |
METHOD FOR FABRICATING A LOCALLY PASSIVATED GERMANIUM-ON-INSULATOR
SUBSTRATE
Abstract
The invention relates to a method for fabricating a locally
passivated germanium-on-insulator substrate wherein, in order to
achieve good electron mobility, nitridized regions are provided at
localised positions. Nitridizing is achieved using a plasma
treatment. The resulting substrates also form part of the
invention.
Inventors: |
Signamarcheix; Thomas; (La
Terrasse, FR) ; Allibert; Frederic; (Grenoble,
FR) ; Deguet; Chrystel; (Saint Ismier, FR) |
Correspondence
Address: |
WINSTON & STRAWN LLP;PATENT DEPARTMENT
1700 K STREET, N.W.
WASHINGTON
DC
20006
US
|
Family ID: |
40085584 |
Appl. No.: |
12/552891 |
Filed: |
September 2, 2009 |
Current U.S.
Class: |
257/616 ;
257/E21.211; 257/E29.068; 438/458 |
Current CPC
Class: |
H01L 21/02252 20130101;
H01L 21/76254 20130101; H01L 21/02247 20130101; H01L 29/16
20130101; H01L 21/318 20130101; H01L 21/02112 20130101; H01L
21/76283 20130101 |
Class at
Publication: |
257/616 ;
438/458; 257/E21.211; 257/E29.068 |
International
Class: |
H01L 29/12 20060101
H01L029/12; H01L 21/30 20060101 H01L021/30 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 3, 2008 |
EP |
EP 08290827.8 |
Claims
1. A method for fabricating a locally passivated
germanium-on-insulator substrate which comprises the steps of:
providing a substrate having at least a germanium (Ge) containing
surface layer as a source substrate, and locally providing
passivated regions on the surface layer for use in forming the
germanium-on-insulator substrate.
2. The method of claim 1, wherein the surface layer of the source
substrate is a silicon germanium layer or an epitaxial Ge layer,
and the locally passivated regions comprise germanium
oxynitride.
3. The method of claim 1, wherein the providing of the passivated
regions includes providing a patterned mask over the source
substrate and nitridizing the source substrate with a plasma.
4. The method of claim 3, wherein the plasma is a NH.sub.3, N.sub.2
or N.sub.2O plasma and which further comprises applying an oxygen
or argon plasma before applying the NH.sub.3, N.sub.2 or N.sub.2O
plasma.
5. The method of claim 1, which further comprising annealing the
locally passivated regions for 1 hour or more at about 600.degree.
C.
6. The method of claim 1, which further comprises providing a
predetermined splitting area in the source substrate, bonding the
source substrate to a handle substrate, and detaching the source
substrate at the predetermined splitting area to thereby obtain the
locally passivated germanium-on-insulator substrate.
7. The method of claim 6, which further comprises activating the
source substrate or the handle substrate, or both, using a plasma
treatment that includes an oxygen plasma or a NH.sub.3, N.sub.2 or
N.sub.2O plasma prior to bonding, and then bonding the substrates
directly after the plasma treatment without any intervening further
process step.
8. The method of claim 6, which further comprises providing a
dielectric layer on the source substrate on the handle substrate,
or on both substrates prior to bonding, wherein the dielectric
layers comprise an oxide.
9. The method of claim 3, wherein the mask is at least one of a
shadow mask that includes Teflon or metal, or a deposited mask that
includes a photoresist or germanium oxide.
10. The method of claim 3, which further comprises providing the
mask by providing a germanium oxide layer on the source substrate,
providing a photo resist layer on the germanium oxide layer, and
nano-imprinting the photo resist layer, and providing the pattern
by plasma or reactive ion etching.
11. The method of claim 1, which further comprises a step of
providing alignment marks on or in the source substrate configured
and arranged to identify the positions of the locally passivated
regions.
12. The method of claim 11, wherein the step of providing alignment
marks comprises a step of providing a pattern of recesses in the
source substrate pattern, with the recesses optional including a
dielectric layer therein.
13. The method of claim 12, which further comprises providing the
predetermined splitting area such that it crosses the recesses in
the source substrate.
14. A method for fabricating a locally passivated
germanium-on-insulator substrate which comprises the steps of:
providing a substrate having at least a germanium (Ge) containing
surface layer as a source substrate, locally providing passivated
regions on the surface layer by providing a patterned mask over the
Ge containing surface layer, and then subjecting the source
substrate surface and mask to a plama or reactive ion etching,
providing a predetermined splitting area in the source substrate,
bonding the source substrate to a handle substrate, and detaching
the source substrate at the predetermined splitting area to thereby
obtain the locally passivated germanium-on-insulator substrate.
15. A germanium-on-insulator substrate comprising a substrate
having at least a germanium (Ge) containing surface layer and
locally passivated regions in or on the Ge containing layer.
16. The germanium-on-insulator substrate of claim 15 which further
comprises alignment marks configured and arranged to identify the
positions of the locally passivated regions.
17. An electronic device comprising nmos and pmos device structures
on or in the germanium-on-insulator substrate of claim 16, wherein
the nmos structures are provided over the localised, passivated
regions, and the pmos structures are provided over other regions of
the germanium-on-insulator substrate.
Description
BACKGROUND
[0001] The invention relates to a method for fabricating a
germanium-on-insulator (GeOI) substrate and a
germanium-on-insulator substrate.
[0002] Germanium-on-insulator structures are generally known in the
art. EP 1 659 623 A1 discloses a method to fabricate a
germanium-on-insulator (GeOI) substrate during which a germanium
oxynitride (GeO.sub.xN.sub.y) layer is provided as a buried
dielectric between a Ge layer and a handle substrate, e.g., a Si
wafer. T. Signamarcheix et al in Applied Physics Letters 93, 022109
(2008) describes the advantageous effect of the presence of a
GeO.sub.xN.sub.y layer underlying the active Ge layer concerning
the electron mobility. Thus, this kind of substrate can
advantageously be used for electronic devices based on n-MOS
technology. It appears, however, that the hole mobility became
affected by the presence of the GeO.sub.xN.sub.y layer so that
concerning p-MOS devices, this kind of substrate is less
suited.
[0003] Accordingly, there is a need for improved
germanium-on-insulator substrates and these are now provided by the
present invention.
SUMMARY OF THE INVENTION
[0004] The invention relates to a method for fabricating a locally
passivated germanium-on-insulator substrate which comprises the
steps of: providing a germanium (Ge) substrate or a substrate
comprising a Ge containing layer, in particular an epitaxial Ge
layer or a silicon germanium layer (SiGe), as a source substrate,
and locally treating the source substrate to provide passivated
regions, in particular regions of GeO.sub.xN.sub.y. With the
inventive method, a germanium-on-insulator substrate with
satisfying electronic properties, in particular high electron
mobility in the passivated zones and hole mobility in the non
passivated regions, can be obtained. In case of a SiGe layer, the
inventive method is particularly advantageous for high Ge contents
of more than 50%, in particular more than 70%.
[0005] Preferably, the passivation of the source substrate, the
surface of which comprises a native Ge oxide which needs to be
stabilized, is achieved by providing a germanium oxynitride
(GeO.sub.xN.sub.y) layer with a substantial nitrogen content of 20
to 50%. With this GeO.sub.xN.sub.y layer, the desired passivation
and the desired improvements concerning electron mobility in the Ge
layer directly above the passivated region in the final substrate,
can be achieved.
[0006] Advantageously, the source substrate can be locally treated
by providing a patterned mask over the source substrate. With this
method, any pattern can be realised on the source substrate so that
the regions which should show a high electron mobility according to
the desired final structures, can be achieved. As an alternative,
maskless patterning methods can also be used.
[0007] Preferably, the passivating can be achieved by nitridizing.
Using this method, advantage is taken of the already present
natural Ge oxide to obtain the GeO.sub.xN.sub.y layer.
[0008] Preferably, the source substrate can be locally treated
using a plasma, in particular a NH.sub.3, N.sub.2 or N.sub.2O
plasma. According to a variant, the NH.sub.3, N.sub.2 or N.sub.2O
plasma can be diluted in 10% to 30% Ar. With this method and in
particular at low pressure, in particular with a plasma of less
than 40 mTorr, preferably in a range of 1 to 10 mTorr, a
significant amount of up to 40% Nitrogen atoms can be incorporated
into the substrate. Optimized results have been achieved for a
pressure of 5 mTorr. This process is preferably carried out at a
temperature of 25.degree. C. up to 600.degree. C.
[0009] Advantageously, the local treatment of source substrate can
further comprise applying an oxygen and/or argon plasma, in
particular before applying the NH.sub.3, N.sub.2 or N.sub.2O
plasma. The oxygen comprising plasma can advantageously be used to
improve and/or thicken the germanium oxide layer on top of the
source substrate. Providing the nitrogen containing plasma after
the oxygen plasma has the advantageous effect of passivating (both
chemically and electronically) the surface of the source
substrate.
[0010] According to a preferred embodiment, the method can further
comprise a step of providing a predetermined splitting area inside
the source substrate before or after the local treatment step.
Preferably, this step includes implanting an atomic species into
the source substrate to form a zone of weakness at which splitting
is intended to occur.
[0011] The inventive method can further comprise a further step of
providing a dielectric layer, in particular an oxide, on the source
substrate before or after the implanting step. In case the
predetermined splitting area is provided after providing the
dielectric layer, the dielectric layer could be at least partially
removed to improve surface quality. In all other cases, the
dielectric layer is used to provide the desired dielectric
properties of the buried layer of the GeOI substrate over the
passivated and non passivated regions of the source substrate. The
local passivation treatment may create a slight surface topology.
Providing the dielectric layer on the locally passivated surface
has the advantage that a planarization step (e.g., by CMP) can be
carried out. This will also form a surface which can easily be
bonded to other substrates.
[0012] In a further preferred variant, the locally passivated
source substrate can be annealed to stabilize the GeO.sub.xN.sub.y
passivation surface, in particular for 1 hour or more at about
600.degree. C. This can be performed before or after the mask
removal. The thermal treatment has the consequence of stabilising
the GeO.sub.xN.sub.y regions and, depending on the mask type used,
also to sublime the mask layer.
[0013] A further method comprises attaching, preferably by bonding,
of the source substrate to a handle substrate, and then detaching
the source substrate at the predetermined splitting area, to
thereby obtain the locally passivated GeOI substrate. With the
stable GeO.sub.xN.sub.y dielectric layer on the source substrate it
becomes possible to transfer a thin Ge layer together with the
GeO.sub.xN.sub.y layer in the nitridized regions to achieve the
desired locally passivated GeOI substrate. The handle substrate is
preferably a silicon wafer.
[0014] Advantageously, the method can further comprise a step of
providing a dielectric layer, in particular an oxide, on the handle
substrate before the substrates are bonded together, in particular
when there is no dielectric provided on the source substrate. In
the case of a silicon wafer, the dielectric can be a thermal oxide
and/or a deposited oxide. Thus, bonding can be achieved between the
locally passivated surface of the source substrate and the
dielectric of the handle substrate, between the dielectric of the
source substrate and the surface of the handle substrate without
dielectric, or between the dielectric layers of the source and
handle substrate.
[0015] According to an advantageous variant, the method can
furthermore comprise a step of activating the handle substrate
using a plasma, in particular an oxygen plasma and/or NH.sub.3,
N.sub.2 or N.sub.2O plasma, in particular mixed with Ar, before the
bonding step. Activating of the handle substrate surface provides
improved bonding between the substrates.
[0016] Preferably, bonding can be carried out directly after the
plasma treatment step is conducted on the source substrate or the
handle substrate without any intervening further process step. By
immediately carrying out the bonding step, a deterioration of the
GeO.sub.xN.sub.y surface can be prevented and superior final
products be achieved. Thus, according to the invention, passivation
of the Ge material and activating of the surface for bonding are
achieved in a single step. Of course, prior to bonding, the
patterned mask needs to be removed.
[0017] Advantageously, the mask used in the mask providing step can
be at least one of a shadow mask, in particular a Teflon mask or
metal mask or a deposited mask, in particular a photo resist based
mask, with a thickness of 1 .mu.m or less or a germanium oxide or
GeO.sub.2 mask. It was found that these types of masks are suitable
to provide the desired locally passivated regions in the source
substrate. Prior to bonding, the mask is removed using, for
example, dry or wet etching, in particular a plasma etching using
N.sub.2, or by a thermal treatment as long as the passivation is
not negatively affected.
[0018] Preferably the local treatment step can comprise the steps
of: providing a germanium oxide or GeO.sub.x layer, which can be
the natural or a deposited one, on the source substrate, providing
a photo resist layer, nano-imprinting the photo resist layer, and
providing the pattern by plasma etching in particular reactive ion
etching (RIE). According to an alternative embodiment, the
GeO.sub.x layer can also be patterned using a laser or electron
beam treatment. Using the nano-imprinting step, locally passivated
structures like islands of a micro- and/or nanometric size are
readily achievable.
[0019] Advantageously, the photoresist layer can be removed before
the local passivation such that the step of removing the
photoresist layer does not have an impact on the locally passivated
regions.
[0020] According to a preferred embodiment, the method can
furthermore comprise a step of providing alignment marks on or in
the source substrate. According to the invention, the substrate
will present areas of the Ge "top" layer that should receive n-MOS
type of devices due to improved electron mobility over the locally
passivated regions and other areas away from the locally passivated
regions are suited to receive p-MOS type of devices as; in those
regions; the hole mobility is better. The alignment marks will
support the steps of manufacturing the n-MOS and/or p-MOS devices
as they provide a reference point so that the various devices can
be formed on their corresponding regions.
[0021] Advantageously, the method can further comprise a step of
providing recesses in the source substrate pattern. The pattern of
the recesses is chosen such that it becomes possible to know where
the buried locally passivated regions are positioned. It is not
necessary to use the same pattern as the one of the passivated
regions as long as positioning of preferably all buried locally
passivated regions is possible.
[0022] According to a further preferred embodiment, a dielectric,
in particular a SiO.sub.2 layer, can be provided in the recesses.
After depositing the SiO.sub.2 layer, a planarization step, e.g., a
CMP step, can be carried out to obtain a surface with SiO.sub.2
islands inside a Ge surface. Based on the properties of the
dielectric, it becomes possible to identify the passivated regions.
Preferably, this dielectric layer is the same as the one described
previously.
[0023] Preferably the dielectric layer can be provided such that
the predetermined splitting area is crossing the recesses of the
source substrate. This has the advantage that the dielectric is
visible on the surface thus the locally passivated regions buried
in the substrate can be identified from outside the substrate.
Preferably, the recesses can have a depth of 0.5 to 2 .mu.m.
[0024] The means for alignment can be provided before or after
providing the locally passivated regions. Providing them before the
passivated regions has the advantage that the fabrication process
concerning the means for alignment does not have an impact on the
locally passivated regions.
[0025] The invention also relates to a germanium-on-insulator
substrate comprising locally passivated regions, in particular,
substrates obtainable according to one or a combination of any of
the methods described herein. With such a germanium-on-insulator
substrate, the above described advantages can be achieved.
[0026] Thus, the invention relates to a germanium-on-insulator
substrate (GeOI) comprising buried passivated regions. According to
a preferred embodiment, the germanium-on-insulator substrate can
furthermore comprise alignment marks, in particular SiO.sub.2
islands, configured and arranged to identify the positions of the
buried passivated regions. Preferably the alignment marks, extend
up to the surface of the GeOI substrate.
[0027] Another embodiment of the invention is an electronic device
comprising nmos and pmos device structures on or in one of the
germanium-on-insulator substrates described herein, wherein the
nmos structures are provided over the localised, passivated
regions, and the pmos structures are provided over other regions of
the germanium-on-insulator substrate. Other electronic devices
incorporating the novel substrates of the invention can be
envsisioned by those persons of ordinary skill in the art. The
substrates that include alignment marks are especially useful in
forming these electronic devices.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Advantageous and preferred embodiments of the invention will
be described in the following text by referring to the drawing
figures, wherein:
[0029] FIGS. 1A-1G show a first embodiment of the method for
fabricating a germanium-on-insulator type wafer according to the
invention,
[0030] FIGS. 2A-2G show a second embodiment of the method for
fabricating a germanium-on-insulator type wafer according to the
invention,
[0031] FIGS. 3A-3G show a third embodiment of the method for
fabricating a germanium-on-insulator type wafer according to the
invention,
[0032] FIGS. 4A-4F show a fourth embodiment of the method for
fabricating a germanium-on-insulator type wafer according to the
invention, and
[0033] FIG. 5 illustrates a fifth embodiment of the invention,
namely an electronic device comprising n-MOS and p-MOS structures
provided on a substrate fabricated a germanium-on-insulator type
wafer according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0034] In the following specification, the overall method for
fabricating a germanium-on-insulator type wafer according to the
invention will be described based on the well known SmartCut.TM.
technology. However, other suitable semiconductor on insulator
providing manufacturing methods can also be adapted to the
invention, for example, a bonding and grind/etch back process.
[0035] FIG. 1A illustrates a germanium (Ge) substrate 1 or, as a
variant, a substrate with a germanium containing layer, in
particular an epitaxial Ge layer or a silicon and germanium
comprising layer SiGe, provided on one of its main surfaces. In the
case of a SiGe layer, the Ge content is preferably at least 50%,
more preferred more than 70%. Prior to further treatment steps, the
surface 3 of the source substrate 1 may be cleaned using, for
instance, a HF base solution (fluoric acid).
[0036] FIG. 1B illustrates a handle substrate 5 which can be, for
example, a germanium wafer, a silicon wafer, a silicon carbide
wafer, a wafer presenting a silicon germanium front surface or a
gallium arsenide wafer. Eventually, also a quartz type wafer could
be used. Both the source substrate 1, as well as the handle
substrate 5, may have any suitable size of form such as, for
example 200 mm or 300 mm type wafers.
[0037] FIG. 1C illustrates steps b) and c) of the inventive method
for fabricating a locally passivated germanium-on-insulator wafer
according to claim 1 which consists of first providing a patterned
mask 7 over the source substrate 1 and then treating the source
substrate 1 via the patterned mask 7 to obtain locally
GeO.sub.xN.sub.y regions 9 in or on the source substrate 1.
[0038] The mask can be a contact mask, thus provided on the source
substrate 1. According to a variant, as illustrated in FIG. 1C, a
non-contact mask positioned above the surface 3 of the source
substrate 1 can be provided. In this case, the mask 7 can be a
Teflon mask or a metal on the source substrate 1.
[0039] The openings 11 in the mask 7 are of micrometric or
nanometric size so that the locally passivated regions 9 of the
source substrate 1 are also in the micrometric or nanometric range.
They can have a regular size or varying size with respect to each
other.
[0040] According to this embodiment of the invention, the treatment
step is a nitridizing step using a nitrogen comprising plasma, in
particular a NH.sub.3, N.sub.2 or N.sub.2O plasma diluted in an
Argon plasma, to incorporate nitrogen atoms into substrate 1.
[0041] Preferably, the plasma is applied for about 60 seconds at
low pressures of less than 40 mTorr, in particular in a range of
1-10 mTorr. The preferred temperature range is 25.degree. C. up to
600.degree. C. Optimized results have been achieved in a pressure
range of 5 mTorr and at temperatures of 150.degree. C. It appears
that the lower the pressure of the plasma, the more nitrogen can be
incorporated. The plasma treatment can be followed by a temperature
treatment around 600.degree. C. This is particularly useful in the
case where the mask 7 is formed of GeO.sub.2. The thermal treatment
has then the consequence of stabilising the GeO.sub.xN.sub.y
regions 9 and also to sublime (to render volatile) the GeO.sub.2
mask layer. This treatment is a surface treatment and the thickness
of the N rich regions is less than 10 nm, preferably less than 5
nm, more preferably 3 nm.
[0042] Actually, due to the presence of oxygen as natural germanium
oxide on the surface of the germanium substrate 1 or in the
environment during the passivation treatment, the nitridizing steps
leads to the creation of GeO.sub.xN.sub.y type islands in those
regions 9. In the final germanium-on-insulator substrate (see
further down), the Ge material of the top layer above those islands
shows a high electron mobility.
[0043] Following the removal of the mask 7, a predetermined
splitting area 13 is provided inside the source substrate 1 as
illustrated in FIG. 1D. The predetermined splitting area 11 is
essentially parallel to the main surface 3, which is provided with
the locally passivated germanium oxynitride regions 9. According to
the SmartCut technology, the predetermined splitting area is
obtained by implanting atomic species 15, for instance hydrogen or
helium ions, with a predetermined energy and dose into the source
substrate 1. According to a variant, this step can also be carried
out before the removal of the mask 7.
[0044] Afterwards, as illustrated in FIG. 1E, a dielectric layer
17, in particular an oxide layer such as a silicon dioxide layer,
is provided, e.g., by deposition, on the source substrate 1. This
layer 17 extends over the entire surface of the source substrate 1,
thus also over the passivated regions 9. Subsequently, a
planarization step could be carried out, e.g., by CMP.
[0045] In a subsequent step, the source substrate 1 with the
nitridized regions 9 and the dielectric layers 17 is attached, in
particular by bonding, to the handle substrate 5 to form a
source-handle compound 19. Bonding occurs between the surface of
the handle substrate 5 and the surface 21 of the dielectric layer
17 (see FIG. 1F).
[0046] FIG. 1G illustrates the result of the detachment step which
occurs at the predetermined splitting area 13. Typically, a thermal
annealing leads to the desired detachment, however other energy
providing means may also be suitable in replacement or in
complement of the anneal. Actually, during annealing, a weakening
of the predetermined splitting area 13 until complete detachment
between the remainder 23 and the newly formed
germanium-on-insulator substrate 25 with locally passivated regions
9 occurs. The inventive germanium-on-insulator substrate 25 with
locally passivated regions 9, comprises the handle substrate 5, the
dielectric layer 17, the passivated regions 9 and a transferred
germanium layer 27. Like already mentioned, the substrate 25 shows
improved electron mobility in the passivated regions and in the non
passivated regions the hole mobility is not negatively affected by
the passivation.
[0047] The remainder 23 of the source substrate 1 can then be
reused as a source substrate 1 in subsequent locally passivated
germanium-on-insulator manufacturing processes.
[0048] According to variants of the first embodiment, the sequence
of the various steps can be changed. Thus, according to one
variant, the ion implanting step illustrated in FIG. 1D is carried
out before creating the nitridized regions 9, thus before the step
illustrated in FIG. 1C. Furthermore, according to a second variant,
the dielectric layer 17 is provided on the nitridized regions 9
before ion implantation. Thus, the step illustrated in FIG. 1E can
be carried out before the step illustrated in FIG. 1D. Eventually,
in this variant, a surface region of the dielectric layer 17 is
removed after ion implantation to improve the surface quality.
According to a third variant of the first embodiment, prior to
applying the nitrogen containing plasma, an oxygen and/or argon
containing plasma can be applied to improve and/or thicken the
germanium oxide layer which is already present on top of the source
substrate 1. The role of the nitrogen containing plasma is then to
activate the surface of the source substrate 1 in the nitridized
regions 9.
[0049] The final product 25 can furthermore receive additional
treatments, such as a polish and/or a heat treatment, to stabilize
the structure.
[0050] FIGS. 2A-2G illustrate a second embodiment of the inventive
method.
[0051] The steps illustrated in FIGS. 2A-2D correspond to the steps
illustrated in FIGS. 1A-1D. Their description is therefore not
repeated again, but incorporated herewith by reference to the
description of FIGS. 1A-1D. The difference between the first and
second embodiments is that, instead of providing a dielectric layer
17 onto the source substrate 1 following the nitridizing step, a
dielectric layer 31, e.g., silicon dioxide, is provided, for
example by deposition or a thermal treatment, on the handle
substrate 5, like illustrated in FIG. 2E.
[0052] The surface 33 of the dielectric layer 31 undergoes an
activation using a plasma, in particular an oxygen plasma and/or
nitrogen containing plasma e.g., NH.sub.3, N.sub.2 or N.sub.2O
plasma. The plasma treatment of layer 31 is carried out under
conditions compared to the plasma treatment conditions of the
source substrate described in detail with respect to FIG. 1C.
[0053] FIG. 2F then illustrates the step of attaching, in
particular by molecular bonding, the source substrate 1 to the
handle substrate 5 to form the source-handle compound structure 33,
In this case, bonding occurs at surface 33 of the dielectric layer
31 and the surface 3 of the source substrate 1 with the passivated
regions 9.
[0054] Just like in the first embodiment, the next step,
illustrated in FIG. 2G, consists in detaching the
germanium-on-insulator type substrate 37 from the remainder of the
source substrate 1 (not shown). The germanium-on-insulator
substrate 37 in this embodiment comprises the handle substrate 5,
the dielectric layer 31, the locally passivated regions 9 and the
transferred layer 27.
[0055] According to a variant, the steps illustrated in FIGS. 2C
and 2D can be exchanged such that the passivated regions 9 are
achieved after providing the predetermined splitting area 13. In
this case, attachment can be carried out immediately after the
plasma treatment on the source substrate 1 and the plasma treatment
on the dielectric layer 31 and an improved stability of the
stoichiometry of the GeO.sub.xN.sub.y regions 9 is observed.
[0056] Of course, the methods according to embodiment 1 and
embodiment 2 can be combined in which case the attachment is
achieved between dielectric layer 17 and dielectric layer 31.
[0057] FIGS. 3A-3G illustrate a third embodiment of providing a
locally passivated germanium-on-insulator substrate according to
the invention. FIGS. 3A-3G illustrate in detail one possibility to
provide a patterned mask and, using this mask, to treat the source
substrate 1 to obtain locally passivated regions 9 on the source
substrate 1. The mask in this embodiment is in contact with the
surface 3 of the source substrate 1.
[0058] FIG. 3A corresponds to FIGS. 1A and 2A, thus represents the
source substrate 1, a germanium wafer or a wafer with a germanium
layer on its surface 3. FIG. 3B illustrates the next step of
providing a germanium dioxide GeO.sub.2 layer 41 on the surface 3
of the source substrate 1. The germanium dioxide layer 41
corresponds to the natural oxide layer or can be a deposited
one.
[0059] The next step consists in providing a photoresist layer 43
on the germanium dioxide layer 41. Subsequently, using a
nano-imprint process known in the art, the photoresist layer 43 is
patterned. Via the patterned photoresist layer 45, a patterned mask
47 is created inside the germanium dioxide layer 43 to play the
role of mask 7, as illustrated in FIG. 1C. Patterning of layer 43
is e.g., achieved by using a reactive ion etching process. As an
alternative, instead of providing the photoresist layer, also a
laser ablation, ion beam or electron beam sputtering process can be
used to create the mask 47 in the germanium dioxide layer 41.
Preferably, the photoresist layer 45 is removed before the
passivation step such that the step of removing the photoresist
layer does not have an impact (removal) on the passivated surface
layer. Via the mask 47, a nitridizing treatment, as described with
respect to FIG. 1C, is then applied to form the nitridized regions
9 in the source substrate 1. The result of this step is illustrated
in FIG. 3F.
[0060] Finally, the mask 47 is removed, e.g., using an N.sub.2
plasma or a thermal treatment at about 600.degree. C. for one hour
or more.
[0061] FIGS. 4A-4F illustrate a fourth embodiment for fabricating a
locally passivated germanium-on-insulator substrate according to
the invention. As already illustrated in FIGS. 1A, 2A and 3A, the
step illustrated in FIG. 4A consists in providing a germanium
substrate 1 or a substrate comprising an epitaxial germanium layer,
such that the surface 3 of substrate 1 is a germanium layer.
Process steps already previously described are not repeated again
in detail, but their description is incorporated herewith by
reference.
[0062] Subsequently, using a mask 51, recesses 53 are provided in
the source substrate 1. These recesses 53 have a depth d.sub.1 and
are, for example, obtained using an etching process such as
reactive ion etching. The recesses 53 have a micrometric depth of,
for example, 1 micron (see FIG. 4B).
[0063] Subsequently, the process step as illustrated in FIG. 1C is
carried out (FIG. 4C), namely the source substrate 1 with the
recesses 53 is treated via mask 7 to obtain locally passivated
regions 55 comparable to the ones 9 illustrated in FIG. 1C.
Actually, the only difference between the locally passivated
regions 55 and the ones 9 illustrated in FIG. 1C is that, now,
these locally passivated regions 55 are provided inside the
recesses 53.
[0064] As a next step (FIG. 4D), a dielectric layer 57, e.g.,
SiO.sub.2, is provided over the source substrate 1 which covers the
locally passivated regions 55 and the recesses 53. To smoothen the
surface of the dielectric layer 57, a polishing step, such as CMP,
is carried out.
[0065] Then, as illustrated in FIGS. 1D and 4E, a predetermined
splitting area 13 is created inside the source substrate 1.
According to the invention, the predetermined splitting area 13 is
created at a depth d.sub.2 being smaller than the distance d.sub.1
of the surface of the germanium substrate down to the bottom 59 of
the recess 53.
[0066] Subsequently, the source substrate 1 with dielectric layer
57 is attached, preferably by bonding, to a handle substrate 5
(like described with respect to FIGS. 1B and 1F) and detachment
occurs at the predetermined splitting area 13 as illustrated in
FIG. 1G. After detachment, the locally passivated
germanium-on-insulator substrate 61, as illustrated in FIG. 4F, is
obtained. As the alignment marks 63 are on the surface of substrate
61, it becomes easy to identify the position of the germanium
islands 65 overlaying the locally passivated regions 55 based on
the fixed positional relationship between alignment marks 63 and
passivated regions (based on their respective masks 7 and 51).
[0067] Embodiments 1-4 can be freely combined to achieve further
variants of the invention.
[0068] The locally passivated germanium-on-insulator substrates 25,
37 and 61, as well as the various variants thereof, find their
application in devices having n-MOS and p-MOS structures fabricated
on a single substrate. In particular, advantage is taken of the
high electron mobility in the passivated regions and the good hole
mobility in the other regions.
[0069] FIG. 5 illustrates the substrate 61 and further electronic
structures. As illustrated in FIG. 5, n-MOS devices 71, 73 are
positioned above the passivated regions 55 (because of higher
electron mobility in this area) and p-MOS devices 75, 77 are
fabricated over the non passivated areas (because of higher hole
mobility). This allows to have a wafer on which both type of
devices can have improved performance. The alignment marks 63 on
the surface are advantageously used to precisely position each
respective device 71, 73, 75, 77 over the specific area of the
substrate 61. Thus superior devices based on germanium-on-insulator
substrates can be fabricated.
* * * * *